Process of treating and utilizing gases and equipment therefor



May 2, 1933. w DARRAH- 1,906,447 PROCESS OF TREATING AND UTILIZING GASESANDEQUIPMENT THEREFOR Filed Jan. 2, 1930 Figure I L Fiy'ure Ill 1Inventor.

Patented May 2, 1933 WILLIAM A. DARRAH, OF CHICAGO, ILLINOIS PROCESS OFTREATING AND UTILIZING AND EQUIPMENT THEREFOR Application filed January2, 1930. Serial N 418,040.

This invention relates to processes and methods for treating andutilizing gases particularly products of combustion and the equipmentnecessary for such treatment or application.

The object of my invention is to utilize gases which may containproducts of combustion and various chemical compounds without incurringobjectionable results owing to the nature of these gases. I may utilizethese gases in baking, drying, heating, heat treating and similarapplications and the gases used may consist of air, carbon dioxide, etc.or products of combustion mixed with air or undiluted.

In order to explain the operation of my invention I will select thespecific case in which the circulating gases contain products ofcombustion with air and possibly water vapor and will assume thatsulphuris the element which subsequently causes diliiculty in utilizingthe products of combustion.

t should be understood that while my description specifically relates tothe case of sulphur in products of-combustion or the so-callcd fluegases yet "similar difliculties may result fromthe presence of compoundsof nitrogen, selenium, tellurium and many other materials. It is wellknown that sulphur when oxidized may form either the dioxide or thetri-oxide depending upon the temperatures of oxidation, Whether or notcatalysts are present, time elapsing between oxidation and the intervalofcooling and other factors.

In the case of drying such materialsas gypsum board, wallboard, paper,fiber board and other similar substances particularly those high incellulose, starch, dextrine and related products, it is desirable tocirculate a quantity of heated gases over'the article from which thewater is being removed. If the gases contain products ofcombustion fromcoal, gas or oil containing large amounts of sulphur it has been foundthat a very troublesomediscoloration of the surface results. Manyattempts have been made to overcome this discoloration but in generalwithout success, as far as I am aware, so that where appreciablequantities of sulphur are present it is customary to separate theproducts of combustion from the circulating gases by means of tubes orother surfaces which serve as heat interchangers. This results in aconsiderable loss of heat in the stack gases and in an increased cost ofequipment for heat interchangers. This 7 also reduces the flexibilityand capacity of the equipment. 7

One of the objects of my invention is to provide means for overcomingthis limitation and to make it possible to intermix the products ofcombustion even though they contain considerable amounts of sulphurwiththe circulating gases thus getting high er economy of operation,lowercost of equipment and other obvious advantages.

In studying this problem I have found that the presence of large amountsof sulphur dioxide in the circulating gases has a relatively smallefiect upon the material being treated. While the presence of evenrelatively small amounts of sulphur trioxide will cause the blackeningwhich has previously been known. In-other words, my experiments haveindicated that the degree of oxidation of the sulphur controlled to alarge extent its effect upon the surface. As

a theory which seems reasonable, I am ofthe 80 opinion that sulphurtri-oxide when brought into contactl'with a wet cool surface, condensesforming with thewater present sulphuric acid which when the properconcentration and temperature is reached, gives a will known blackeningeffect.

On the other hand, in the case of sulphur dioxide this material maycondense on the surface of the board, but sulphurous acid is formedwhich not only does not darken the board but may under certainconditions, serve as a bleaching agent.

On observing this phenomenon I have therefore devised means forconverting the sulphur tri-oxide which is present in products ofcombustion to sulphur dioxide and have found that when this step istaken considerable amounts of sulphur may be present in the fuel withoutseriously affecting the material being dried. My invention, therefore,covers not only a method of successfully using products of combustionhigh in sulphur, but also means for converting the form. of the sulphuroxide into one which is comparatively harmless.

I wish it to be distinctly understood that while this discussion refersspecifically to sulphur and its oxides yet similar means may be utilizedin thecase of oxides of nitrogen, selenium and other materials whichoccasionally contaminate fuels.

I have found that in the oxidation of sulphur under the conditions whichexist in an ordinary combustion chamber, considerable quantities of boththe dioxide and the trioxide are simultaneously produced. I have alsofound that at high temperatures in the presence of an excess of oxygenwhich practic'ally always exists when fuel is burned completely, thedioxide may be converted to the tri-oxide or the reaction may bereversed. The higher the temperature in general the more rapid theconversion in either direction.

I have also found that as a result of this fact a rapid cooling ofintensely hot products of combustion results in an increased percentageof sulphur tri-oxide and a reduced percentage of sulphur dioxide. Conversely a slow rate of cooling results in an increase in the percentageof sulphur dioxide and a reduction in the percentage of sulphurtri-oxide.

I have also found that if the gases are cooled in contact with a metalsurface such as iron, 1r0n alloys, etc., the percentage of sulphurtri-oxide is still further reduced with a corresponding increase in thepercentage of sulphur dioxide.

Utilizing the results of these discoveries, I have therefore devisedmeans for burning fuel and for subjecting the products of combustion toa relatively gradual cooling, preferably in contact with metal surfaceswhich are cooler than the gases themselves.

Referring now to the drawing:

Figure 1 shows a verticalelevation in sec tion across my furnace anddryer taken along the lines I-I, of Figure 8.

Figure 2 shows a longitudinal section of the vertical elevation. Figure2 is taken on section line IIII, of Figure 3.

Figure 3 shows a plan view partly in section of one form of my furnaceapplied to the specific case of a dryer.

It is understood that the drawings are diagrammatic and illustratemerely one way of applying the elements of my invention.

In the drawing 1 represents a shell or housing which may be formed ofbrick with a layer of insulation 2 and covered by a roof 3. A dryerhousing 4 is shown located beside the heater housing 1. The dryer may beof the roller type in which a series of live driven rolls indicated by 5serve to convey the material. On the other hand, I may use a series ofcars, trays, chains or other conveying device, or I may place thematerial to be dried into the dryer by hand and remove it as desired.These obvious modifications all fall within the scope of my invention.For the purposes of illustration I have shown a roller dryer providedwith a series of feed rolls 6 at the entering end and a series ofdischarge rolls 7 at the leaving end. For ease in delivering thecirculating hot products of combustion and air I provide longitudinalducts 8 and 9 along the sides of the dryer and in order to control theflow of circulating gases I divide these ducts at an intermediateportion by partitions 10 and 11 respectively. A'fuel supply device 12 islocated near the end of the combustion chamber 13 in heater housing 1and serves to supply the necessary fuel and air. This may be taken torepresent a gas burner, oil burner, powdered coal burner or otherdesired device as obviously my invention is not restricted to anyparticular type of burner. In order to obtain durability and a heattransfer I prefer to construct combustion chamber 13 from a refractorymaterial having a fairly good heat conduc tivity. Some materials I havefound satisfactory are silicon carbide, aluminum oxide, heat resistingalloys, such as nickel chromium alloys and similar products although Ihave used ordinary fire clay in certain cases with satisfactory results.For ease of mechanical construction in order to avoid too lengthy adevice I have found it convenient to build the combustion chamber in twochambers. A lower portion is indicated by 13 and an upper portionindicated by 14. As a further convenient means for cooling the productsof combustion in contact with metal I provide a series of metal tubes 15connected to the combustion chamber by means of a flue 16. As aconvenient means of construction I apply a tube sheet 17 into which oneend of the tubes may be fastened. The tubes may be supported in anyconvenient manner and the opposite end from the tube sheet is left open.A series of baflies indicated by 18, 19, 20, 21, 22 and 23 are providedto direct the circulating atmosphere within the heater housing 1 aroundand over the tubes. It should be understood that where I refer to tubesI do not necessarily mean a round or cylindrical device gases then passthrough nozzles 30 and 31 and flow between the layers of rollers 6 beingbrought into close contact with the materials being dried. The gasesthen flow in the direction shown by the arrows leaving dryer 4 andentering return duct 32. They then pass through branches 33 and 34 intoair spaces 35 and 36 on each side of the combustion chamber. Gases thenpass upward over the surface of the combustion chamber withdrawing aportion of heat from the combustion chamber.

These gases continue to travel andpass over and around tubes 15 thusremoving heat from the surface of these tubes. The gases finally travelforward along the length of heater 1 and around the tubes until inmixing chamber 37 they are drawn into the products of combustion leavingtubes 15. No effort is made to thoroughly mix the products of combustionleaving tubes 15 with the gases which return outside the tubes as theirtemperatures are substantially equal and a variation in chemicalcomposition is of no particular importance. The gases when mixed thencontain portions of the products of combustion, through duct 28 into fan24 and begin the cycle again.

The excess of gases, due to the continuous addition of products ofcombustion and the water vapor formed in the drying operation may escapefrom the ends of the dryer or through stacks or ducts as desired, notshown.

Referring now to the operation of this device it will be noted that thecombustible material delivered into combustion chamber 13 ignites and aconsiderable quantity of heat is withdrawn through the walls ofcombustion chamber 13 and transmitted to the circulating gases outsidethese walls. The cooler products of combustion then travel into space 14above combustion chamber 13 and give up still-more of their heat contentto the circulating gases outside the combustion chamber. The products ofcombustion next pass through the fine 16 and then through tubes 15 wherethey are cooled to the desired temperature in contact with the surfaceof the tubes and ample opportunity is given for sulphur tri-oxide to bereduced to sulphur dioxide both by the gradual ire- These circulatingduction in temperature and by the contact with the metal surface whichacts as a socalled negativecatalyzer.

It will be evident, therefore, that the de-' vice I have provided offersmeans for burning the fuel, reducing" the temperatureof the products ofcombustion at a pre-determined rate and while doing so bringing saidproducts of combustion into contact with a surface which acts as anegative catalyzer.

In some cases I have found it an advantage to place within the ducts ortubes 15 a seriesof widely separated surfaces as for example a tangle ofwire or the equivalent, so that the products of combustion are allbrought into close contact with a metal surface. In this case the wiremay be made from a heat resisting alloy although the material from whichit is formed will of course depend on the temperature to which it-issubjected. It should be understood that I may or may not use the tangleof wire or other means such as metallic wool, etc.

While I have disclosed one specific form in which my invention may beembodied, I wish it to be clearlyunderstood thatfnany changes may bemade in the mechanical arrangement, size, shape and disposition of thevarious parts without departing from the spirit of my invention.

It will be noted that my invention provides means for cooling productsof combustion in more or less continuous successive'stages. Thedegreelof cooling and the rate of cooling as well as the exact meansemployed will of course depend onthe results which must be obtained. Forexample a flame which would ordinarily produce relatively lowtemperature as for example a producer gas flame would require lesscooling and would even for the same percentage of sulphur ordinarilycontain lower quantities of sulphur tri-oxide. On the other hand, aflame formed from heavy fuel oil would require careful treatment inorder-"to tri-oxide. The process andthe device which I have disclosedmaybe adapted to'any of these conditions by those skilled in the art byproperly proportioning the sizes, surfaces, materials and otherconditions to meet the requirements of each individual case.

"It should be understood that it is ordinarily unnecessary to reduce thetempera ture of the products of combustion down to the so-calledroom'temperature. In many cases where these are reduced to 400 or 500the desired commercial result is accom plished. I, therefore,do notrestrict this invention to any particular scale of temperatures.

In using the term negative catalyzer I wish to specifically include allsubstances which have atendency to break down the higher oxide compoundsinto other compounds. Many such. materials are known and to recite theentire list would result in excessive extension of this applicationwithout accomplishing a useful purpose. Only a few specific cases ofthese negative catalyzers have been cited, but they are well known inthe art. In addition to the metallic surfaces discussed I may also usesuch materials as lime, barium oxide and a wide range of oxides which atthe temperatures discussed serve to accomplish the desired result.Certain of the materials specified are more useful in specific casesthan others, but the nature of the gases to be treated, the nature ofthe impurities, the operating temperatures, permissible velocities andmany other factors control the selection of the negative catalyzer.

Having now fully described my invention what I claim as new and wish tosecure by Letters Patent in the -United States is as follows:

1. The process of treating products of combustion containing acidforming oxides which consists in gradually reducing the temperature ofsaid products of combustion in an oxidizing atmosphere and bringing saidproducts of combustion into contact with a basicrcompound foraccelerating the reduction of acid oxides to a lower form of oxide.

2. The process of treating hot gases which consists in reducing thetemperature of said gases under oxidizing conditions while in contactwith a basic oxide.

3. The process of treating hot gases containing acid forming oxideswhich consists in cooling said gases under oxidizing conditions incontact with an alkaline material.

4. The process of treatingproducts of combustion containing gaseoussulphur compound which consists in cooling said proclucts of combustionprogressively in an oxiidizing atmosphere and maintaining said productsof combustion in contact with a material having an alkaline reaction forat least a portion of the cooling period.

5. The process of treating hot gases containing sulphur oxides whichconsists in cooling said gases progressively and maintaining said gasesin an oxidizing atmosphere in contact with an iron containing alkalinesurface for a portion of the cooling period.

6. The process of treating products of combustion containing gaseouscompounds of sulphur which consists in cooling said products ofcombustion progressively in an oxidizing condition, maintaining saidproducts of combustion in contact with lime during a portion of saidcooling period and finally mixing said treated products of combustionwith other gases.

7. The'process of de-oxidizing hot gaseous acid. forming compounds whichconsists in cooling said gaseous compounds progressivelyunder oxidizingconditions and bringing said gaseous compounds in contact with limeduring a portion of the cooling period.

8. The process of converting sulphur trioxide into sulphur dioxide whichconsists in subjecting a portion of hot gases containing said sulphurtri-oxide under oxidizing conditions to a progressive cooling undercontrolled conditions, in contact with basic material.

9. The process of converting sulphur trioxide into sulphur dioxide whichconsists in subjecting a portion of hot gases containing said sulphurtri-oxide to a progressive cooling under controlled temperatureconditions in an oxidizing atmosphere and bringing said sulphurtri-oxide into contact with an alkaline material during a portion ofsaid cooling period.

10. In the process of treating products of combustion containing gaseoussulphur compounds, the step of progressively cooling said products ofcombustion under oxidizing conditions while in contact with an alkalinematerial.

11. In the process of treating products of combustion containing gaseoussulphur compounds, the step of progressively cooling said products ofcombustion under oxidizing conditions while in contact with a metalsurface, and an alkaline material.

12. A device for treating combustion gases which contain acid formingmaterials which consists of a housing, a. combustion chamber within saidhousing, a burner device cooperating with said combustion chamber and anair passage in said housing, a cooling duct connected to said combustionchamber said cooling duct being formed for a portion of its length tosupport a solid alkaline material in contact with said gases to betreated.

13. A device for treating combustion gases containing acid formingmaterial which consists of a housing, a combustion chamber within saidhousing a burner device cooperating with said combustion chamber andcooling duct connected to said combustion chamber, means for coolingsaid duct by circulating gases and means for supporting solid alkalinematerial in contact with said gases being treated and means for mixingsaid gases being treated with said circulating gases, and a gas movingdevice for re moving treated gases from said housing.

14. A device for treating combustion gases containing sulphur compoundsconsisting of a housing, a combustion chamber within said housing,cooling ducts connected to said combustion chamber, means for supportingalkaline material in contact with said gases while being cooled and apassageway around said coolingducts and communicating with an opening insaid cooling ducts.

15. A device for treating gases which consists of a housing, arefractory combustion chamber Within said housing, a burner cooperatingtherewith, a metallic cooling chamber connected to said combustionchamber and containing alkaline material passages around said coolingduct and communicating with said cooling duct, and means for removingsaid treating gases from said housing.

WILLIAM A. DARRAH.

